SCOTS actor Gerard Butler got into amazing shape for the epic film 300, which is based on Frank Miller's graphic novel, but only after being told he was too fat to play the lead.

The Tomb Raider and Phantom Of The Opera star plays King Leonidas, leader of a 300-strong army of Spartans, pitted against a huge army of Persians in the Battle of Thermopylae 2500 years ago.

Gerard was so determined to live up to the lead role, he began training three months before he was asked to turn up for the film company's scheduled boot camp sessions.

Butler, 36, admitted: "When I went into this film I was in really bad shape. I had just come from Italy and three different people who I had never met before had commented on me being fat.

"I got the role shortly after the film got the go ahead and I had made a promise to myself that I would make this the film of my life, so I went a little crazy.

"The boot camp for the movie was very intense but I had already been training for three months before that.

"I had my own trainer six-days-a week doing two hours a day working on weights and cardio.

"I was running and circuit training but then I started doing it with Mark Twight, who is a mountain climber who trains other climbers, cage fighters and undercover operatives. The guy is just insane.

"We would do a lot of circuit training using a lot of primitive tools like kettle bells, medicine balls, rings and huge elastic things which attached to the wall. You would have to run and then stop and hold. I also worked with the stunt people in an non-air conditioned warehouse and that was like an oven inside. That was the stuff that really made you sweat. I was pretty much naked and the floor would be soaking wet with our sweat.

"By the time I went into boot camp I was already into pretty good nick, but the boot camp was still tough."

The result is an incredible six pack physique which Butler says was needed if he was going to get his fellow actors and the audience to believe he could lead an army to their deaths.

But Gerard admits the work it took to get back into shape really took its toll.

He said: "Afterwards I had tendonitis in almost every part of my body. I had a bad injury in my forearm which still comes up if I go back into the gym.

"I had a rotator cuff injury and I pulled my hip flexer. Then there was a lot of whacks. Whenever you're doing a lot ofsword fighting you're always getting whacked in the head or punched."

Those schooled in the classics will remember the Battle of Thermopylae from their history lessons because the root of Western civilisation itself was at stake.

Staged in a mountain pass, the heroic last stand by 300 Spartans saw them outnumbered by King Xerxes' invading 80,000 strong Persian army in 480BC.

For three long days, the Spartans inflicted appalling losses on the Persians before they were eventually outflanked and killed.

But their bravery and sacrifice inspired all of Greece to unite and drive the Persians from their land which then paved the way for the birth of democracy.

While Butler plays Leonidas, British actors such as rising star Lena Headey in the role his wife, Queen Gorgo, and Dominic West as the warrior Theron, help make up some of the cast of 300.

Like Miller's comic book, the violent battle scenes in the £30million movie are filmed entirely on a blue screen background and is shot in monochrome rather than in colour. Computergenerated special effects feature terrifying monsters, carnage on the battlefield and incredible superhuman fight scenes.

Critics who have seen the film say it is one of the goriest movies they have ever seen, while Hollywood hopes 300 will revitalise a genre which has waned since Ridley Scott's Oscar-winning Gladiator, seven years ago.

Butler was determined to make sure he wouldn't be lumped in with those weedy English and American actors who get picked for roles just for their looks and are then asked to play battlehardened warriors.

He said: "It's easy for me to be paranoid, especially when you're an actor playing the lead role. I have previously seen so many actors with a massive amount of armour on and then these little twiggy arms.

"I'm not naming any names, but some of them have these plummy accents and you think to yourself: 'You couldn't fight your way out of a paper bag and you're commanding armies or are supposed to be a knight or whatever. That's all so King Arthur.

"I wanted to be the guy who my men could look to and say: 'Yeah, I would follow him.' And the audience would look at him and think: 'Yeah, I can see why they would follow him into battle.' And then finally, that I would be feeling like: 'Of course they're going to follow me.'

"I also wanted to see that in their eyes, that I could feel they had respect for me.

"These guys were stunt men. They were amazing to us. So I never really played like I was their king. I just got in among them and we became friends and we went out together.